Hair-styling tool



Dec. 2, 1969 H. s. couRNoYER 3,481,345

HAIR-STYLING TOOL Filed sept. 14, 1965 United States Patent O HAIR-STYLING TOOL Hector S. Cournoyer, Miami Beach, Fla., assignor, by

mesne assignments, to Grooming Developers, Inc., Chicago, Ill., a corporation of Illinois Filed Sept. 14, 1965, Ser. No. 487,173

Int. Cl. A45d 24/00 U.S. Cl. 132-149 13 Claims ABSTRACT F THE DISCLOSURE A hair-styling tool produced by a method in which resilient metal prongs having terminal notches or grooves are oriented in parallel relation at random and a handle is molded about one end of the oriented prongs and grooves so that the prongs will be retained in the molded handle thereabout, and the exposed grooves or notches are so dimensioned that they will not snarl or impede movement of the prongs through human hair.

This invention relates to hair styling and is directed particularly to an improved hair-styling implement used for creating fantasy'or highly styled coiffures. In particular, this invention relates to novel improved hair-styling implement constructions embodying my invention of United States Letters Patent No. 3,148,686 issued Sept. 15, 1964 (to Hector S. Cournoyer), and to novel improved methods for making the same.

Applicant has been a cosmetologist for about ten years, including with leading beauty and high style hair dressing salons in Miami Beach, Fla. Thus, applicant has long been fully familiar with the problems of long-used prior techniques and implements for working and shaping womens hair to create fantasy and other high-style coiffures having desired external appearance, especially on a quick and efficient basis. (See, for example, discussion in my aforementioned U.S. Patent No. 3,148,686 filed Mar. 14, 1963.)

More particularly, for many years, when working with bouffant and high-style coiffures, it was the practice of accomplished and leading hair stylists to use miscellaneous make-shift devices such as hair pins, stiff rattail combs, etc., to work womens hair from the inside to the surface to achieve the desired appearance. This, however, was time-consuming, inefficient and unsatisfactory; and the shortcomings of such piror techniques and devices for working bouffant and other high-style coiffures were widely recognized by skilled hair stylists for many years, including applicant and his many associates in the field. Various efforts were made to more efficiently and satisfactorily perform such hair styling with various sorts of implements; but, because they were designed for other purposes, they did not provide satisfactory results (according to my knowledge or information as of the time I made said invention and filed application for patent thereon).

The above-discussed problems and shortcomings of prior techniques and implements for achieving high-style coiffures have been very effectively solved by my novel hair-styling implement invention utilizing the embodiments of my aforementioned Patent No. 3,148,686 issued Sept. 15, 1964. In fact, novel improved hair-styling implements embodying the invention of my Patent No. 3,148,- 686 have in a short time proven to be very successful in actual use by professional skilled hair stylists, for rapidly and efficiently achieving high-style coiffures of attractive appearance with elimination of snarling, discomfort and other annoyances to the patron and the stylists. Further, these novel improved hair styling implements embodying the invention of my Patent No. 3,148,686 have even ICC proven remarkably useful for do-it-yourself high style hairdos by untrained women.

Thus, hair-styling implements embodying the invention of my aforementioned Patent No. 3,148,686 have quickly achieved widespread commercial success in the United States and elsewhere with minimal advertising particularly in early days when applicants available funds were very litimed). Communications to applicant and his assignee show the enthusiastic acceptance of my invention of Patent No. 3,148,686 by professional hair stylists and other accomplished and trained personnel in the beauty supply field resulted from rapid conviction, through their expertise, of the advantages and merits of these novel improved hair-styling implements embodying the invention of my Patent No. 3, 148,686. To my knowledge and information, many skilled hair Stylists, and established distributors of hair-styling implements in the United States and Canada have already abandoned prior make-shift and other unsatisfactory hair-styling implements in favor of these new improved hair-styling implements embodying the invention of my Patent No. 3,148,686. Similarly, the demonstrable advantages of these novel hair-styling implements embodying the invention of my Patent No. 3,148,686 led to quick acceptance by women for home hairdos and substantial retail sales. In fact, applicant and his assignee, Cournoyer Industries, Inc. of Miami, F1a., have received many unsolicited testimonials from professionals and non-professionals regarding the performance and advantages of my novel patented hair-styling implement.

The substantial rapid acceptance by professionals and non-professionals achieved by these hair-styling implements embodying the linvention of my Patent N0. 3,148,- 686, and the resultant volume of sales generated, has led to further efforts by applicant to provide improved methods for efficient mass production of consistently high quality hair-styling implements embodying my patented invention. After considerable time, effort and expense, it was found this involved an interplay of: (l) factors relating to efficient production of a hair-styling implement with resilient pronged teeth and handle embodying the in- -vention of my Patent No. 3,148,686; (2) the marketing and related economic pressures dictating resort to one standard design for mass production to market throughout the United States; and (3) the problem of achieving a single standard design of womens hair-styling suitable for use by millions of American women is aggravated by the fact that American women stem from so many different national origins, whereby the hair of American women varies even more than the variation of hair in a comparably large number of women of the same ethnic background. Thus, a single standardized hair-styling implement model made in large quantity by a suitable mass production method must meet a surprising number of interacting and inconsistent requisites for marketing throughout the United States, and Canada, and even other foreign countries.

Accordingly, it is a principal object of the invention of this application to provide certain further novel improvements in the construction of hair-styling implements with resilient pronged teeth embodying the invention of my Patent No. 3,148,686 to overcome such interacting factors and problems discussed above; some additional new embodiments of my patented hair-styling mplement achieving a single model suitable for marketing in the beauty field throughout the United States, Canada, and even other foreign countries; and novel methods for rapidly and economically making such hair-styling implements of desired construction and consistently uniform quality at low cost, even using relatively unskilled operating personnel.

It is also an object of the present invention to provide a new further improved hair-styling implement embody- -ing my patented invention, whereby the resilient pronged teeth incorporated therein may be in the form of wire prongs made efficiently and at minimal cost from wire coil by existing machinery and which may be firmly and reliably imbedded in an injection-molded plastic handle by means of grooves of suitable configuration adjacent the end of the wire prongs imbedded in the handle of the implement. It is another related object of the present invention to provide an improved embodiment of the hairstyling implement of my Patent No. 3,148,686 wherein reliable mass production is facilitated by using such wire prongs provided with like grooves adjacent both prong ends, to eliminate the problem or need for properly orienting and preassembling for molding, as in the case of prongs having a single grooved end which must `be oriented and aligned in the proper direction to 'be imbedded in the molded handle. It is another related object to eliminate the serious quality control problems and increased costs resulting due to inattention or other shortcomings of the pre-assembler, molder, checker and other production personnel, and also avoiding backfire and losses in marketing due to loss of prongs because the single grooved end of even one such prong is not imbedded in the molded plastic handle.

However, after developing the above-discussed improvements in construction and method of manufacture, it was discovered that providing grooves at both ends of such wire prongs resulted in the catching, snagging and snarling of womens hair during the working of a hairdo due to said grooves at the free ends of the wire prongs. Accordingly, another important object of the present lnvention is to provide novel improved embodiments of my hair-styling implement invention of Patent No. 3,148, 5

686 which can be made by the above-discussed new and more efficient methods, yet takes into account the interplaying and inconsistent factors of mass production, nationwide marketing of a single standardized model hairstyling implement suitable for a wide range of variation of womens hair, the use of resilient wire prongs having grooves adjacent both ends for firmly imbedding same in the molded handle, and designing the grooves at the free ends of the prongs so as to not catch or snarl the hair, or otherwise impede manipulation of the wire prongs of the implement through the hair. It is a related object to provide such a single model implement for styling hair which does not incur dissatisfaction in professional or non-professional use, notwithstanding the wide variation in womens hair throughout the United States and elsewhere.

The aforementioned and other more specific objects and advantages of the present invention will become apparent from the following description thereof in conjunction with the accompanying drawings, and the appended claims.

In the drawings:

FIGURE 1 is a perspective view of the new, improved hair-styling implement embodying the invention of my Patent No. 3,148,686, and incorporating above-discussed additional improvements in construction for improved methods of production, as disclosed and claimed in this application.

FIGURE 2 is an illustrative perspective view of half of an injection mold showing an array of wire prongs disposed therein for firmly imbedding one grooved end of the prongs in a portion of the injection molded handle (the other half of the mold being illustrated in phantom line in this figure).

FIGURE 3 is an enlarged elevation view of a single (enlarged about 32 times actual size), illustrating the relationship of a strand of hair (H) shown in cross section with respect to a groove of arcuate cross section formed in the prong near bo-th ends, the arcuate cross section of this figure being a preferred version.

FIGURE 5 is a fragmentary enlarged longitudinal sectional view similar to that of FIGURE 4, but showing the relationship of a hair (H) in cross section to a groove formed in the prongs adjacent both ends, with said grooves having a V-shaped cross section as illustrated in FIG- URE 5 (this being an alternative embodiment as amplified below).

FIGURE 5A is an illustrative somewhat schematic enlargement of part of FIGURE 5, for clear illustration with respect to certain important size limitations amplified below.

FIGURE 6 is a fragmentary enlarged longitudinal sectional view similar to that of FIGURE 4, but showing the relationship of a hair (H) in cross section to a groove formed in the prongs adjacent Vboth ends, with said grooves having a trapezoidal shape cross section as illustrated in FIGURE 6 (this being an alternative embodiment as amplified below).

FIGURE 6A is an illustrative somewhat schematic enlargement of part of FIGURE 6, for clear illustration with respect to certain important size limitations amplified below.

FIGURE 7 is a fragmentary enlarged longitudinal sectional view similar to that of FIGURE 4, but showing the relationship of a hair (H) in cross section to a groove of rectangular cross section formed in the prongs adjacent both ends, (this being an alternative embodiment as amplified below).

Referring particularly to FIGURES 1 and 2 of the drawings, there is shown a new improved embodiment of my hair-styling implement, generally indicated at 10, comprising a molded plastic handle generally indicated at 12 and an array of like wire prongs generally indicated at 14.

The handle 12 is made of any commercially available plastic material suitable for injection molding, and it generally is made with an indented portion 16 on at least one side, and preferably on both sides, to assure a firm grip of the tool handle by the operator. The handle 12 also includes a lower edge portion 18 which is of suitable size and thickness (see axes x and y in FIG. l) to provide sufiicient mass for firmly imbedding the terminal ends of metal prongs 20 in injection molded handle portion 18.

Referring now particularly to FIG. 2, this illustratively shows at 24 one half of a suitable injection mold. The mold half 24 includes a body portion 26 having an inner surface 28 adapted to mate with the inner surface of a like second mold half 24' indicated in phantom lines. The mating surfaces 26 of each of like mold halves 24 and 24 are provided with a plurality of elongated prong receiving grooves 30 extending from one end 32 of mold half 24, and 24') to a transversely extending portion 33 of a handle forming recess 34 formed in mating mold face 26 and shaped to produce a handle section 16 of desired configuration. The handle forming recess 34 in each of mold sections 24 and 24 is in communication with a gate 35 through which the plastic is injected according to the established injection molding practices.

Referring particularly to FIGS. 1-3, each of the multiple wire prongs 20 used to manufacture the improved hair styling implement 12 is provided with a pair of like grooves 22 formed near each end of the prong, with configuration and dimensions being according to criteria more fully set forth below. The grooves 22 at one end of the wire prongs 20 extend into the transverse mold groove 33 as shown particularly in FIG. 2 to provide means for firmly anchoring the array of prongs 14 in the molded plastic handle 16, due to the plastic fiowing into and setting within the grooves 22 of prongs 20 during the injection molding process.

For high volume production, one would generally use a multiple cavity injection mold comprising a mold body having a plurality (e.g. 4) mold cavities such as provided by mold 24-24 of FIG. 2, in a manner apparent to those skilled in the art in light of the foregoing. In volume production according to the present invention, for better quality control, a suitable holder having drilled apertures to hold the Wire prongs 20 is used to preassemble prongs so as to locate in substantially the same plane the end of all prongs 20 in an array 14 whereby the grooves 22 to be imbedded in the plastic handle section 18 are also substantially aligned. This holder is used to insert the array 14 of wire prongs 20 into the prong receiving recesses 30 of mating mold sections 24 and 24 so that the grooves 22 at the molded end of each prong 20 are automatically disposed in alignment at the proper location within the transverse mold groove 33 forming handle portion 18 to firmly imbed the wire prongs 20 in the injection molded handle portion 18. This substantially eliminates problems of loosening or loss of prongs when the improved implement is used for hair styling, and even when the implement may be carelessly manipulated, or abused by tossing into a tray, or be subjected to other thoughtless or unskilled useage.

The provision of annular grooves 22 adjacent both ends of each wire prong for making the improved hair implement 10 greatly facilitates production and quality control, since this eliminates problems of proper orientation in pre-assembly and molding, whereas unskilled and relatively low cost workers will frequently fail to properly orient such wire prongs having a groove adjacent only one end so that all grooves will be disposed within the transverse section 33 of molds 24 and 24 to assure all wire prongs 20 of array 14 are firmly imbedded within handle portion 18. A preferred commercial embodiment of applicants invention for professional hair styling use incorporates six prongs, whereby failure of the pre-assembler and/or molder to properly orient only one out of six prongs grooved at only one end results in scrapping of the entire molded implement 10. This not only results in substantial loss of time, money and effort in abortive production, but also causes additional loss in removing prongs from the handle of rejects to reclaim the plastic, with the removed wire prongs usually being rendered unfit for use. Another serious problem is quality control, as noted above.

Thus, the use of wire prongs having at both ends grooves of suitable configuration and seize to securely imbed the array of prongs 14 in the plastic handle portion 18 at both ends provides important production and quality control advantages, reduces costs, etc. as discussed. However, it was found the above-described hair styling implement 10 made by means of the above-discussed irnproved method created problems in use, and thus in marketing, because the resultant presence of grooves 22 adjacent the free ends of the wire prongs 20 objectionably caught and snagged hair in use. It was also found that the size and/or configuration of grooves 22 formed adjacent both ends of the Wire prongs for efiiciently making the hair styling implement 10 could not be indiscriminate due to interplay of factors relating to optimum production procedures and problems in marketing and use of this type hair styling implement, particularly in the case of a single standardized .hair styling implement for sale throughout the United States, Canada and even foreign countries for reasons discussed above.

It has been found from experience that such interplaying factors relating to optimum construction for most eicient and reliable production methods, with minimum quality control, etc., as against optimum performance in hair styling, minimizing snagging and catching of hair and other marketing problems, etc., should be balanced by making the new improved hair-styling implement 10 according to the following criteria:

(1) The plastic handle 12 of the hair-styling implement should be approximately two inches in width (per direction y in FIGURE 1).

(2) The exposed length of the wire prongs 20 extending from below handle portion 18 should be at least about two inches in length, e.g. 2% to 31/2 inches.

(3) The diameter of metal wire prongs 20 should be about .025 to .050 inch. (A suitable material for wire prongs 20 is 302 stainless steel, spring hard, which may be economically processed to prepare prongs 20, as amplified below.)

(4) It has been found that the most suitable crosssectional shape for annular grooves 22 formed adjacent both ends of wire prongs 20 is an arcuate shape as illustrated in FIG. 4 (preferably a circular arc or portion thereof, or a comparable smooth arc), configuration and dimensions being consistent with further more detailed criteria set forth below.

(5) It has also been found that annular grooves 22 adjacent both ends of wire prongs 20 may alternatively have, subject to proper dimensioning set forth below, a V-shaped cross section as in FIG. 5, a trapezoidal cross section as in FIG. 6, or a rectangular cross section as in FIG. 7 (the preference of such alternative embodiments of FIGS. 5, 6 and 7 generally being in said numerical order, after that of FIG. 4).

(6) Both ends of wire prongs 20 should have a rounded or comparable configuration, such as illustrated in FIG- URES 4-7, to insure that metal prongs 20 of the hairstyling imple-ment 10 may be inserted and moved through a womans hair to lift and arrange hair Without harming the scalp or irritating the person.

(7) Each of grooves 22 per FIGURES 1-4 (and corresponding grooves identified by numerals 22a, 22h, and 22e in FIGURES 5, 6 and 7, respectively, for convenient discussion) should be suitably located, e.g. about V32 to 5/32 of an inch, from each of the two free ends 38 of wire prongs 20.

(8) Subject to preferred narrower limits discussed below for each of the specific embodiments of FIGURES 4, 5, 6 and 7, made with different cross-sectional grooves 22, 22a, 22h and 22C, it has been found that the axial dimension of such grooves adjacent both ends of wire prongs 20 (dimension w in each of FIGURES 4-7) may vary from about 0.003 to 0.012 inch, but that it is preferable that this axial dimension wl of said grooves adjacent both ends' of prongs 20 vary between about 0.005 to 0.008 inch, although it may as large as about 0.012 inch.

(9) Subject to preferred narrower limitsdiscussed below for each of the different specific embodiments of FIGURES 4, 5, 6 and 7, respectively, it has been found that the radial depth of such grooves adjacent both ends of wire prongs 20 (dimension D in each of FIGURES 4-7) should be preferably between labout .003 to .005 inch, although it has been found feasible on a large volume production basis to accommodate Variations of groove depth D from between 0.001-0.002 inch to 0.007-0.008 inch.

(l0) Referring particularly to FIGURE 4 showing an enlarged end of a wire prong 20 provided adjacent both ends with groove 22 having an arcuate cross section as discussed above, the radial depth D of grooves 20 in this embodiment should be about 0.0015 to 0.002 inch, and the axial dimension w should be about 0.003 to 0.004 inch, for optimum balance of production, usage, and marketing factors, for national and even international marketing of a single model.

(11) Referring to FIGURES 5 and 5A, showing an enlarged free end section of a wire prong 20a having a groove 22a of V-shaped cross section, it has been found that both the angle A 'and the depth D of V-shaped groove 22a should be such that the axial dimension w at the locus of half the radial depth D, per FIGURE 5A, is less than .003 inch, for optimum balance of factors referred to in paragraph 10 above, when using this alternative configuration.

(12) Referring to FIGURES 6 and 6A showing an enlarged free end of a Wire prong 20b provided with a groove 22b of trapezoidal cross section, it has been found that the dimension of the small base of the trapezoid, the angle B of the sloping sides, and the depth D should be such that the axial dimension w at the locus of half the radial depth D, per FIGURE 6A, is less than about 0.003 inch, for optimum balance of factors discussed in paragraph above, when using this alternative configuration.

(13) Referring to FIGURE 7, showing an enlarged free end of a wire prong 20c having a groove 221e of rectangular cross section, the axial dimension w should preferably be less than about 0.003 inch and the radial depth D preferably should be less than about 0.003 inch.

(14) Handle section 18 may have a thickness of about 1A; to 1A inch (per axis z in FIGURE l) and an axial length of about 1A; to 5/8 inch (per axis x in FIGURE 10) to assure reliable imbedding of the array 14 of wire prongs 20.

(15) The wire prongs 20, 20a, 2Gb and 20c may be made with such grooves at both ends from suitable metal wire coils on an Escomatic machine which draws and straightens the coil, and cuts the wire to length, rounds the ends, and forms the grooves to make such prongs, as above discussed. There will be some variation in the `configuration and depth of such grooves adjacent both ends of such wire prongs when thus made on a low cost mass production basis, with resultant departures from preferred configuration and dimensions set forth above, due to such factors as wearing of the groove-forming tool during production of a large number of units. E.g., a newly formed tool cuts such prong grooves more closely to desired configuration and dimension, with variation such as decrease in groove depth D as the tool wears. Thus, while tool wear decreases the depth of such grooves in a manner favorable from the viewpoint of the free end optimum design of wire prongs in nationwide usage of a single model hair-styling implement 10, this should not proceed to an extent rendering the grooves at the other end of the prongs unsatisfactory for reliably imbedding them in the plastic handle section 18, as above discussed. Also, as will be apparent, the configuration of the groove will vary from precise semicircular, V-shape, trapezoidal, or rectangular configuration, due to practical limits on economical tool-making, wear etc. However, it has been found that by making the new improved hair styling implement embodying the invention of my aforesaid Patent No. 3,148,686 according to the criteria herein set forth, particularly observing overall limitations such as here discussed, the new improved hair-styling implement construction 10, and the disclosed method of making the same, achieve the production, usage and marketing objectives and advantages discussed, for feasible nationwide and international marketing of a single model.

(16) It has been found that good results can be obtained with an array 14 of six wire prongs, preferably of equal length and at least about two inches long, with the two outer prongs being adjacent the sides of handle portion 18 and the intermediate prongs being substantially equally spaced therebetween as shown; this arrangement has been found very satisfactory for professional hair-styling use. Another arrangement found suitable for home use is a comparable hair-styling implement 10 .having four prongs with two of them adjacent the sides of handle 12 and the other two interspaced at substantially equal distances. Other prong arrangements may also be used, eg., as discussed in my aforementioned Patent No. 3,148,686.

It will be apparent from the foregoing that the present invention provides a new improved hair-styling implement embodying the invention of my Patent No. 3,148,686 with additional improvements in construction, mode of operation and result, and particularly lending itself to a new improved method of manufacture, with related improvements in both construction of the hair-styling implement,

and method of achieving the many advantages above discussed.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive.

What is claimed and desired to be secured by United States Letters Patent is:

1. An implement for arranging human, hair, comprising: a handle of molded material; a plurality of elongated resilient wire prongs, each of said prongs having grooves of like configuration and size formed adjacent each end thereof, with one grooved end of said prongs imbedded in said molded handle, whereby said prongs also have a groove adjacent the free end thereof; said like grooves adjacent each end of said prongs being of such configuration and size that the first mentioned grooved ends of the prongs are firmly imbedded in the molded handle and the second mentioned grooved free ends of the prongs will not catch or snag normal human hair when said implement is used to manipulate human hair.

2. A hair-styling implement for arranging human hair, as defined in claim 1, wherein the dimension of said grooves axially of said prongs is between 0.003 to 0.012 inch, and the radial depth of said grooves in said wire prongs is between about 0001-0002 to about 0007-0008 inch.

3. A hair-styling implement for arranging human hair, as defined in claim 1, wherein the dimension of said grooves axially of said prongs is between 0.005-0.008 inch, and the radial depth of said grooves in said wire prongs varies from between 0001-0002 inch to about 0.005 inch.

4. A hair-styling implement for arranging human hair as defined in claim 2, wherein each of said grooves adjacent both ends of said wire prongs has a substantially rectangular cross section with an axial dimension w less t-han about 0.003 inch and a radial depth D less than about 0.002 inch.

5. A hair-styling implement for arranging human hair as defined in claim 2, wherein the diameter of said metal wire prongs is about 0.025 to 0.050 inch.

6. A hair-styling implement for arranging human hair, as defined in claim 2, wherein said grooves in said prongs are located about 1,;/52 to 732 inch from each end of said prongs.

7. A hair-styling implement for arranging human hair, as defined in claim 2, wherein the plastic handle is approximately two inches wide and the portion of said handle in which said first mentioned grooves of said prongs are imbedded is approximately 1/s to 1A inch in thickness for an axial length of at least 1A to 5A; inch.

8. A hair-styling implement for arranging human hair, as defined in claim 2 wherein the length of said wire prongs extending from said molded handle is at least about two inches.

9. A hair-styling implement for arranging human hair,

as defined in claim 2, wherein both ends of said wire prongs are of sufficiently rounded configuration to prevent the free ends of said wire prongs from harming or irritating the scalp of a human when the implement is used for manipulating or styling human hair. 10. An implement for arranging human hair, comprislng: a handle of molded material; a plurality of elongated resilient wire prongs, the improvement wherein each of said prongs have formed-portions of like configuration and size formed adjacent each end thereof, with one formedportion of said prongs imbedded in said molded handle, whereby said prongs also have a formed-portion adjacent the free end thereof; said like formed-portions adjacent each end of said prongs having such configuration and size that the first mentioned formed-portions of the prongs are firmly imbedded in the molded handle and the second mentioned formed-portions of the prongs adjacent the free ends thereof will not catch or snag normal human hair when said implement is used to manipulate human hair.

11. A hair-styling implement for arranging human hair, as defined in claim 2, wherein eaoh of said grooves provided adjacent both ends of said wire prongs has a substantially arcuate `cross section with -a radial depth D of about 00015-0002 inch and an axial dimension w 0f about 0.003-0004 inch.

12. A hair-styling implement for arranging human hair, as defined in claim 2, wherein each of said grooves provided `adjacent both ends of said wire prongs has a Substantially V-shaped cross section with the angle A and depth D of said V-shaped grooves being such that the'axial dimension w at the locus of half the radial groove depth D is less than 0.003 inch.

13. A hair-styling implement for arranging human hair, as defined in claim 2, wherein each of said grooves adjacent both ends of said wire prongs has a substantially 10 trapezoidal cross section, with the dimension of the small base of the trapezoid, the angle of the sloping sides B, and the radial depth D being such that the axial dimension w at the locus of half the radial depth D is less than about 0.003 inch.

References Cited UNITED STATES PATENTS 2,270,528 l/ 1942 Kirschenbaum. 3,026,146 3/1962 Szabo et al. D. 206,476 12/ 1966 Courno-yer.

LOUIS G. MANCENE, Primary Examiner I. W. MITCHELL, Assistant Examiner 

